’n‹…˜f¯‰ÈŠwêU@’n‹…‰ÈŠwçt‡•”“Á•Êu‰‰‰ï “ú: •½¬‚Q‚T”N‚RŒ‚U“úi…j‚P‚SF‚O‚O@`@‚P‚VF‚O‚O êŠF‹“s‘åŠw —ŠwŒ¤‹†‰È‚P†ŠÙ‚TŠK‚T‚U‚R†º u‰‰‘è–¼[1]F Gouge, glass and gel: the complex origin of amorphous phases during faulting u‰‰ÒF Joseph Clancy White, Department of Earth Sciences, University of New Brunswick, Fredericton, New Brunswick, CANADA u‰‰—v|F Amorphous silicate phases are widely found along brittle faults and within gouge zones. Rotary friction experiments at moderate to high velocities have produced amorphous phases, sometimes coeval with dramatic slip weakening. In light of the latter, gel formation has been proposed as a potential mechanism of slip weakening during earthquakes in the shallow crust; however, low velocity sliding experiments have also produced significant amounts of amorphous material distributed within discrete slipping layers, bringing into question the uniqueness of the mechanism formation. In natural examples, these amorphous phases may form by comminution and hydrolization of silica-rich wall rocks, while others may form by depressurization and boiling of aqueous fluids during fault valving. Silica-saturated hydrothermal fluids released during faulting may contribute in some cases. Analytical scanning transmission electron microscope (STEM) has been used characterize the nano- to micro-structural evolution of the fault -related amorphous and cryptocrystallized material from several faults for comparison with experimental results. u‰‰‘è–¼[2]F Why it causes Mw7 or Mw8? -New Stiffness Hypotheses, result from IODP Costa Rica Drilling Exp344 (2012)- u‰‰ÒF Arito Sakaguchi, JAMSTEC-IFREE, Yokohama, Japan u‰‰—v|F Variations in earthquake magnitude and recurrence intervals of fault behavior need to be understood in the context of regional tectonics. Convergent margins may be divided into two end-member types that are termed erosive and accretionary plate boundaries (e.g. von Huene and Scholl, 1991; Clift and Vannucchi, 2004). The Nankai accretionary margin has a 1300-year historical earthquake record with a recurrence interval of 100-150 years (Ando, 1975). In contrast, the Middle America trench offshore Costa Rica erosive margin have caused with magnitude as high as 7.6Mw every several decade years. CRISP (Costa-Rica Seismogenesis Project) Program-A has carried out the first step toward the deep riser drilling by characterizing the shallow lithologic, hydrologic, stress, and thermal state of this area (Vannucchi et al., 2011; Harris et al., 2013). CRISP drilling of Exp. 344 reveals that the shallow basement of upper plate crust is composed of terrigenous sediment accumulated at a high rate. Costa Rica seismogenic zone is characterized by the subduction of young oceanic crust with high heat flow and active fluid flow (Spinelli and Wang, 2008; Spinelli and Harris, 2011; Harris et al., 2010). These are similar with Nankai seismogenic zone (Kinoshita et al., 2008). Some differences exist between both margins including the convergence rates, the thickness, the composition of incoming sediments and physical properties. Among them, P-wave velocity of upper plate in Costa Rica margin (Stavenhagen et al., 1998) is much higher than Nankai margin (Nakanishi et al., 2002). In frictional stick-slip system, the recurrence interval and event displacement varies with the stiffness of the system. We propose that the characteristic magnitude of large subduction earthquakes and recurrence intervals are influenced by the stiffness of the upper plate. This hypothesis may be best tested at the Nankai and Costa Rica margins. –â‚¢‡‚킹æF “cã ‚LE—Ñ ˆ¤–¾